June 01, 2006

Archaic contribution to modern human populations

PLoS Genetics has an article on the possible contribution of genetic material from archaic humans into the modern human gene pool. I have often before stressed the contribution of Paleoafrican populations into the more recent branch of the sapiens lineage ("Afrasians") which emerged in eastern Africa. This new study seems to support the idea of absorption of older African populations by modern humans.

It is clear that the small early modern human population must have inhabited a correspondingly small geographical region, so it is not surprising that in their movements within Africa they would have interbred with the pre-existing humans. After all, humans lived in Africa for a long time before the emergence of the moderns, and there is no reason to believe that all the African branches of humanity were wiped out to be replaced by the advancing moderns. I predict that in the coming years, we will learn much more about the different strata of genetic ancestry contained in Africans, as well as Europeans and East Asians.

Note, also, that there is no candidate for the source population of the archaic contribution of West Africans. This, again, is not surprising, because western Africa has a much less advantageous climate than eastern Africa for bone preservation, in addition to being less well researched. Even in Europe, where anthropological science is the oldest, and cave surveys have been numerous, there are still only a handful of well-preserved Neanderthal specimens. Hopefully, some of the archaics of Africa remain to be discovered.

From the paper:

While the putative source population may not be as obvious as in Europe (Neanderthals), the fossil record shows that transitional forms of Homo were widespread in Africa, even after the time of emergence of modern humans. Other genetic studies have also found evidence for ancient structure in African [28, 29, 30]. In two of the three studies [28, 30], the divergent lineage was found only in Pygmies, which suggests that the African population source differs from the European one.

PLoS Genetics (early online)

Possible ancestral structure in human populations

Vincent Plagno, Jeff D. Wall

PROVISIONAL ABSTRACT

Determining the evolutionary relationships between fossil hominid groups such as Neanderthals and modern humans has been a question of enduring interest in human evolutionary genetics. Here we present a new method for addressing whether archaic human groups contributed to the modern gene pool (called ancient admixture) using the patterns of variation in contemporary human populations. Our method improves on previous work by explicitly accounting for recent population history before performing the analyses. Using sequence data from the Environmental Genome Project, we find strong evidence for ancient admixture in both a European and a West African population (p ~ 10^{-7}), with contributions to the modern gene pool of at least 5%. While Neanderthals form an obvious archaic source population candidate in Europe, there is not yet a clear source population candidate in West Africa.

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